Combustible fuel

ABSTRACT

The invention discloses a combustible fuel including a compressed unit of crushed maize cob, such as corn cob or white or yellow maize cob, and a method of its manufacture. The corn cob has no additional non-biomass additives and results in a residue of less than 2% by mass after complete combustion.

FIELD OF INVENTION

[0001] The present invention relates to combustible fuel.

[0002] More particularly, the present invention relates to a combustible fuel manufactured from a biomass resource, such as corn cobs, and a method of producing the combustible fuel.

BACKGROUND TO INVENTION

[0003] Combustible fuels are widely used to generate heat for various uses, such as for combined heating and power or cooking. Although fossil fuels such as coal are very efficient heat generators, they produce environmentally undesirable fumes and gasses during combustion. These gasses can also be absorbed in food that is being cooked and taken in by consumption. It is believed that these fumes may have certain harmful effects.

[0004] For the above reasons it is desirable to use a combustible fuel that produces relatively small amounts of undesirable fumes and gasses. Such a combustible fuel has been found to exist in biomass resources, such as in some forestry or agricultural residues. A further advantage is that the biomass resources are normally readily available.

[0005] The use of biomass resources as fuels has been described in U.S. Pat. No. 3,635,684 where Seymour provided a composite fuel article comprised of particulate consumable material, such as ground corn cobs and husk material, a petroleum derivative, such as paraffin slack wax, a lignosulfonate, and a corn starch. The constituents are heated, mixed together and compressed to form a solid fuel article in the shape of a log or briquette. The applicant is of the opinion that the inclusion of the petroleum derivatives or wax and the lignosulfonate lead to the formation of undesirable and environmentally unfriendly gaseous products during combustion.

[0006] In U.S. Pat. No. 4,236,897, Johnston provides a high heating value, fuel pellet comprising from about 50 to about 99% by weight natural cellulose material and from about 1 to about 50% by weight synthetic polymeric thermoplastic material. Again, the use of plastics material leads to the formation of undesirable and environmentally unfriendly gaseous products during combustion.

[0007] A process for preparing combustible solid fuel from grain residue is disclosed by Paquette in U.S. Pat. No. 4,314,825. The process includes the steps of passing the grain residue through a pelletising zone wherein the residue is subjected to compaction pressure of greater than about 100 psi while passing live steam there through for a period sufficient to cause the in-situ cellulose to form a cohesive pelletised mass. Paquette specifically teaches the use of grain residues obtained after milling of the grain and does not use biomass resources that are removed or discarded prior to the milling process.

[0008] In U.S. Pat. No. 4,324,561 Dean et al disclose a process and apparatus for pelletising tree bark and other botanical material for use as an industrial fuel. A dryer burning fines from the final product is used to heat bark or other botanical material which is typically a waste product from lumbering or agricultural production. Once dried, the material is finally ground, preheated and forced through a pelletising mill to create a pelletised product for substituting coal as a heating source. This process requires a large amount of energy to heat the material and may not be economical to operate.

[0009] It is an object of the invention to suggest a combustible fuel, which will assist in overcoming the abovementioned problems.

SUMMARY OF INVENTION

[0010] According to the invention, a combustible fuel includes a compressed unit of crushed maize cob.

[0011] The maize cob may be selected from a group containing a corn cob, a yellow maize cob and a white maize cob.

[0012] The crushed maize cob may be compressed to a density of between 0.25 to 1.5 g/cm³.

[0013] The combustible fuel may, after combustion thereof is completed, produce a residue of less than 2% by mass.

[0014] The combustible fuel may include suitable ignition additives.

[0015] The combustible fuel may include a corn starch as a binding agent.

[0016] The combustible fuel may be adapted to fully ignite within about seven minutes.

[0017] The combustible fuel may be pre-burned in an oxygen depleted atmosphere.

[0018] The combustible fuel may be provided in any shape, e.g. disc-shaped.

[0019] The combustible fuel may be adapted to produce less than 3 minutes smoke emission during combustion for a period of at least 30 minutes.

[0020] Also according to the invention, a combustible fuel includes a corn cob, which is pre-burned in an oxygen depleted atmosphere to form a charcoal.

[0021] The maize cob may be selected from a group containing a corn cob, a yellow maize cob and a white maize cob.

[0022] The combustible fuel may, after combustion thereof is completed, produce a residue of less than 2% by mass.

[0023] The combustible fuel may include suitable ignition additives.

[0024] The combustible fuel may be adapted to fully ignite within about seven minutes.

[0025] Further according to the invention, a method of manufacturing a combustible fuel unit includes the steps of crushing at least one maize cob; of dry mixing the crushed maize cob(s) with a binder to produce a combustible fuel mixture; and of compressing a volume of the combustible fuel mixture to form a combustible fuel unit.

[0026] The method may include the step of crushing the maize cob to a size of between 150 microns and 15 mm.

[0027] The method may include the step of adding a suitable ignition additive to the combustible fuel mixture.

[0028] The method may include the step of heating the combustible fuel mixture to reduce its moisture content.

[0029] The method may include the step of compressing the combustible fuel mixture under a pressure of between 35000 kPa and 176000 kPa.

[0030] The method may include the selection of the maize cob from a group containing a corn cob, a yellow maize cob and a white maize cob.

[0031] The invention also extends to a method of generating heat using a combustible fuel as set out herein.

BRIEF DESCRIPTION OF DRAWINGS

[0032] The invention will now be described by way of example with reference to the accompanying schematic drawings.

[0033] In the drawings there is shown in:

[0034]FIG. 1 a perspective view of a combustible fuel unit in accordance with the invention; and

[0035]FIG. 2 a block diagram of a method of manufacturing a combustible fuel unit shown in FIG. 1.

DETAILED DESCRIPTION OF DRAWINGS

[0036] Referring to FIG. 1, a combustible fuel unit in accordance with the invention, generally indicated by reference numeral 10, is shown. The combustible fuel unit 10 includes crushed or granulated particles 12 of maize cob.

[0037] The maize cob 12 can be a corn cob, a yellow maize cob or a white maize cob, which is compressed into a pellet of desired shape, e.g. disc-shaped, to a density of between 0.25 to 1.5 g/cm³.

[0038] The particles 12 are held together in a matrix of binding agents, such as corn starch, and suitable ignition additives, for aiding in igniting the maize cob during use.

[0039] Once ignited, the combustible fuel unit 10 is adapted to fully ignite within seven minutes. Furthermore, during combustion the combustible fuel unit 10 produces less than 3 minutes smoke emission during a period of combustion of 30 minutes. The mass loss on ignition for the fuel unit 10 was measured as being 99.2%.

[0040] Biomass fuels are characterized by their moisture content, density, apparent density, and what is called the “Proximate and Ultimate analyses”. They can be burned directly for heat or to make steam for power. The “proximate” analysis gives moisture content, volatile content (when heated to 950° C.), the free carbon remaining at that point, the ash (mineral) in the sample and the high heating value (HHV) based on the complete combustion of the sample to carbon dioxide and liquid water. (The low heating value, LHV, gives the heat released when the hydrogen is burned to gaseous water, corresponding to most heating applications.) (Cf. “Thermal Data for Natural and Synthetic Fuels”, S. Gaur and T. Reed, Marcel Dekker, 1998.)

[0041] The energy production of various samples of the combustible fuel unit 10 was tested using a bomb calorimeter. The samples were constituted by finely ground, medium ground and course ground cob particles 12 mixed with or without a corn starch binding matrix. The values given in Table 1 below are lower heating values as received (LHV_(ar)): TABLE 1 Sample Description Calorific value 1 Finely ground particles with starch additive 14.564 MJ/kg 2 Medium ground particles with starch additive 15.187 MJ/kg 3 Finely ground particles without starch additive 15.122 MJ/kg 4 Medium ground particles without starch 15.486 MJ/kg additive 5 Rough ground particles without starch additive 15.712 MJ/kg

[0042] As can be seen from the test results, the average calorific value is about 15.2 MJ/kg. In comparison the lower heating values as received (LHV_(ar)) of charcoal is 23.711 MJ/kg and that of coal is 26.621 MJ/kg.

[0043] Higher heating values, including higher heating values of inter alia corn cob char and other fuels (HHV_(daf)) are given in Table 2: TABLE 2 HHV_(DRY) HHV_(DAF) (MJ/kg) (MJ/kg) ENERGY FUELS Eucalyptus Camaldulensis 19.42 19.57 Casuarina 18.77 19.12 Poplar 19.38 19.64 Sudan Grass 17.39 19.04 AGRICULTURAL Peach Pits 20.82 21.04 Walnut Shells 20.18 20.29 Almond Prunings 20.01 20.34 Black Walnut Prunings 19.83 19.99 Corncobs 18.77 19.03 Wheat Straw 17.51 19.22 Cotton Stalk 18.26 19.57 Corn Stover 17.65 18.69 Sugarcane Bagasse 17.33 19.53 Rice Hulls 14.89 18.75 Pine Needles 20.12 20.43 Cotton Gin Trash 16.42 19.93 SOLID FUELS Coal - Pittsburgh Steam 31.75 35.40 Charcoal 34.39 35.45

[0044] The combustible fuel unit 10 is consumed by about 98% by mass during combustion and produces an ash residue of less than 2% by mass after combustion is completed. An analysis of the residue after combustion of a combustible fuel unit 10 showed the results in Table 3: TABLE 3 Fe₂O₃ 0.08% MnO 0.01% Cr₂O₃ 0.01% V₂O₅   0% TiO₂ 0.02% CaO 0.04% K₂O  0.3% P₂O₅ 0.04% SiO₂  0.1% Al₂O₃   0% MgO   0% Na₂O   0% Cl  0.08% S  0.07%

[0045] Referring now to FIG. 2, a method of manufacturing the combustible fuel unit 10, generally indicated by reference numeral 14, is shown. The method 14 includes a first step 16 wherein a maize cob is crushed to a size of between 150 microns and 15 millimetres. Thereafter in the step indicated by numeral 18 the crushed maize cob is dry mixed with a binder to produce a combustible fuel mixture. Additional additives, such as ignition additives, can be added to the mixture at this time.

[0046] This combustible fuel mixture is heated if required, as shown in an intermediate step 20, to reduce its overall moisture content to less than 12%.

[0047] Finally, in step 22, a volume the combustible fuel mixture is compressed to form the combustible fuel unit 10. A pressure of between 35000 and 176000 kPa is applied to ensure that a solid combustible fuel unit 10 having a density of between 0.25 and 1.5 g/cm³ s obtained.

[0048] As a further step, the combustible fuel unit 10 can be formed into a charcoal briquette by burning the combustible fuel unit 10 in an oxygen depleted atmosphere to form a charcoal, so that many of the impurities are removed and leaving a structure consisting mainly of carbon.

[0049] The combustible fuel unit 10 can alternatively include a complete corn cob, which is turned into charcoal by burning it in an oxygen depleted atmosphere, so that many of the impurities are removed and leaving a structure consisting mainly of carbon.

[0050] The combustible fuel unit 10 can thereafter be burned to generate heat, such as in cooking, heating, power, and combined heating and power. As the combustible fuel unit 10 is made of maize cob, very few environmentally undesirable fumes are produced. Also, as the combustible fuel unit 10 is almost completely consumed during combustion, very little waste is produced.

[0051] The combustible fuel unit 10 can be provided in any colour, e.g. for providing aesthetically more appealing colours than the normal black briquette currently commercially available. 

1. A combustible fuel including a compressed unit of crushed maize cob.
 2. A combustible fuel as claimed in claim 1, in which the maize cob is selected from a group containing a corn cob, a yellow maize cob and a white maize cob.
 3. A combustible fuel as claimed in claim 1, in which the crushed maize cob is compressed to a density of between 0.25 to 1.5 g/cm³.
 4. A combustible fuel as claimed in claim 1, which, after combustion thereof is completed, produces a residue of less than 2% by mass.
 5. A combustible fuel as claimed in claim 1, which includes suitable ignition additives.
 6. A combustible fuel as claimed in claim 1, which includes a corn starch as a binding agent.
 7. A combustible fuel as claimed in claim 1, which is adapted to fully ignite within about seven minutes.
 8. A combustible fuel as claimed in claim 1, which is pre-burned in an oxygen depleted atmosphere to form a charcoal.
 9. A combustible fuel including a corn cob pre-burned in an oxygen depleted atmosphere to form a charcoal.
 10. A combustible fuel as claimed in claim 9, in which the maize cob is selected from a group containing a corn cob, a yellow maize cob and a white maize cob.
 11. A combustible fuel as claimed in claim 9, which, after combustion thereof is completed, produces a residue of less than 2% by mass.
 12. A combustible fuel as claimed in claim 9, which includes suitable ignition additives.
 13. A combustible fuel as claimed in claim 9, which is adapted to fully ignite within about seven minutes.
 14. A method of manufacturing a combustible fuel unit including the steps of crushing at least one maize cob; of dry mixing the crushed maize cob(s) with a binder to produce a combustible fuel mixture; and of compressing a volume of the combustible fuel mixture to form a combustible fuel unit.
 15. A method as claimed in claim 14, which includes the step of crushing the maize cob to a size of between 150 microns and 15 mm.
 16. A method as claimed in claim 14, which includes the step of adding a suitable ignition additive to the combustible fuel mixture.
 17. A method as claimed in claim 14, which includes the step of heating the combustible fuel mixture to reduce its moisture content.
 18. A method as claimed in claim 14, which includes the step of compressing the combustible fuel mixture under a pressure of between 35000 kPa and 176000 kPa.
 19. A method as claimed in claim 14, in which includes the selection of the maize cob from a group containing a corn cob, a yellow maize cob and a white maize cob. 